Burner control system



June 23, 1942. L HOLMES 2,287,248

BURNER CONTROL SYSTEM -Fi1d March so, 1940 \00 A32 Ion EB M Fig 2 Ifinnenfor Gifforl I. Holmes GWHM Patented June 23, 1942 stares BURNERCONTROL SYSTEM 7 p v Gifford ll. Holmes, Minneapolis, Minn, assignor toMinneapolis-Honeywell Regulator Company, Minneapolis, Minn, 'acorporation of Delaware Application March 30, 1940, Serial No. 327,060.

12 Claims.

The present invention relates to burner con-- trollers and moreparticularly to circuits including safety switches for an oil burner.

In systems of the class to which the instant control circuits apply,wherein a timer is adapted to trip a safety switch, dangerous conditionsoft times occur when the timer fails. Timers which must be positivelymoved as a result of the application of heat by a heaterprove extremelyhazardou for practical use because the heaters may burn out. Manysystems have been proposed which operate upon the principle of heatdissipation to move a timer. element is normally heated and, upon a callfor heat by the spacethermostat, the heaterwlll be deenergized to allowsaid element to cool to thereby start the burner.

In such systems the That is, the moving device i protected againstburning out of the heater. However, if a power failure should occur, dueto a burned out fuse, or a failure at the 1 source of power, the devicewill go out on safety.

Inasmuch as such power failures are quite frequent, it is desirable touse asafety switch which will not be placed out of operation because ofsuch failure.

An object of this invention is to provide a simplified and eflicientburner controller which obtains a maximum of safety.

Another object of the present invention is to provide a simplifiedburner control system which obviates the above recited difiiculties. v Afurther object is to provide an improved safety switch which times thetrial ignition period for an oil burner.

Another object is to provide a combustion responsive device incombination with a timer which will render a burner motor inoperative ifthe combustion responsive device fails to respond properly to thepresence or absence ofv combus-v tion. A further object is to provide atimer'which times the trial ignition period by utilizing a heatdissipating actuating element.

, Another object is to provide a combustion controller which timesthe'trial ignition period by the cooling of a control element which isheated when the burner is not in operation, cooled when the, burner isplaced into operation, heated if combustion is properly established, orcooled to break the burner motor circuit if combustion is not properlyestablished.

Still another object, in connection with the last preceding object, isto provide such a controller whichwill break the burner motor circuit ifa heater for the timer burns out, butwill not 3 break the burner motorcircuit in the event that i tion.

Referring more in detail to the drawing a motor H1 is shown which isadapted to operate an oil burner, a gas valve, or the like. An ignitionmeans H is adapted to ignite'the fuel which is delivered by the motorwhen in operation. Electrical energy is supplied from line wires I2 andI3 to the motor and to the ignition means.

The circuit to the motor I0 and theignition means II is controlled by athermostat l5. This thermostat is suitable for location in a space inwhich the temperature is to be controlled. The thermostat 55 comprises abimetal l6 which is suitably secured to some suitable mounting means(not shown) by pin IT. The bimetal I6 has an arm l8 to which a snapacting switch, such as a mercury switch I9 is secured. The mercuryswitch is rendered snap acting by a'suitable indentation in the centerof the bottom thereof and has contacts 20 and 2| which are bridgedbythemercury 23 when the bimetallic element I6 is cooled. Another pairofelectrodes. 24 and metallic element It is hot.

A safety switch mechanism 30 is provided to break the circuit to themotor I0 and to' the ignition means I! in the event that an abnormalcondition occurs, for example, failure of combustion or failure of theburner to start upon a callfor heat by the thermostat IS. The safetyswitch 30 comprises a relatively stiff contact blade 3| and a relativelyflexible contact blade 32 which is normally biased away from the blade3| so that contact 33 and 3 mounted on the blade will be held apart ifblade 32 is released. A suitable heat motor is provided to maintain thecontacts 33 and 34 in engagement for normal operation of the heatingsystem. In the present instance this heat motor comprises a bimetal 35which engages an insulating block 32a carried upon the contact blade 32.The bimetal 35 is mounted upon a. compensating bimetal 36 by a bracket31. The lower end of the bimetal 36is bimetal 36 and the merit whichextends into or a device which is arranged so that a. tempera coldcontact thermostat I is in suitably secured to a mounting bracket 39which may be suitably secured to a switch case (not shown). Thebimetals= 35 and 36 are so arranged that they will warp in oppositedirections upon the application of heat to both of the bi-- metals. Byso arranging the bimetals any deflection of the upper part of thebimetal 35 due to changes in ambient temperature will be compensated forby the bimetal 36.

The bimetal 36 has a heater 40 located adjacent thereto whichv isconnected across the line wires i2 and i3 by electrical conductors 4|and 42. The bimetal 36 is selected so as to flex toward the right asshown in Figure 1 upon the application of heat thereto by the heater 40.In the'event of a failure in the source of electric power which suppliesenergy l2 and I3, the bimetallic element 36 will warp toward the left.The bimetal 35 is provided with a heater 45 which is arranged adjacentthereto and is adapted to supply heat to the bimetal 35 under control ofthe thermostat l5 and a combustion responsive device generally indicatedat 46. The bimetal heaters 40 and 45, is adapted to act as an ignitiontiming means.

The combustion responsive device 45 may be a conventional device whichhas a bimetallic elethe stack of a furnace,

ature responsive element will respond directly to the radiant heat of aflame present in the furnace upon the occurrence of combustion. Forillustration purposes the combustion device 46 which is shown comprisesa switch arm 41, 48, and a hot contact 49. The cold contact 48 will beengaged by the contact arm 41 when there is no rlame present in thecombustion chamber and the contact 49 will be engaged by the contact arm41 when combustion is present in the combustion chamber.

An ignition controller is carried by the bimetal 35. This controllercomprises a press back contact blade 53 which is adapted to engage acontact 5| when the bimetal 35 is heated up to a predetermined value. Ahook 52' is adapted to engage the upper to open the contact 5| when thebimetal 35 cools off. A resistance member 53 is placed in circuit by'thecombustion responsive device 46 to control the circuit to the heater45to cause the bimetal 35 to cool off a suflicient amount to open thecontact 5| in a manner more fully described.

Operation in the position shown the the satisfied, or hot, position and,the electrodes 24 and 25 are bridged by the mercury 23. A circuit isthen established for the heater 45 for the bimetal.35 as follows: Fromthe line wire |2 to the conductor 55, switch blade 3|, contact 33,contact 34, switch blade 32, conductor 56, electrode 24, mercury 23,electrode 25, conductor 51, contact 48, contact arm 41, conductor 58,heater 45, and conductor 59 to the other line wire l3. 'Energization oft e heater will maintain the bimetal 35 in the position shown beneaththe insulating piece 32a on the contact blade 32 and the contacts 50 and5| closed.

Assuming now that the thermostat l5 cools oil to rotate the mercuryswitch l9 toward the right and cause the mercury 23 to pass rapidlyacross With the device the indentation m the bottom of the switch,toysto the line wires 35, in cooperation with the open the contacts 24and 25 and close the contacts 20 and 2|. A circuit for the burner motormay then be traced as follows: From the line wire |2 through conductor55, switch blade 3|,

contacts 33 and 34, switch blade 32, conductor 56, electrodes 20 and 2|through the mercury 23, conductor 60, conductor 6|, the burner motor l0,and conductor 62 to the other line wire l3. Also a circuit for theignition means maybe traced from the conductor 60 through the conductoras, contact 5|, contact blade 50, conductor 64, ignition means II, andthe conductor 65 to the other line wire l3.

When the circuit for the burner motor and ignition is established thecircuit for the heater 45 through the hot contacts 24 and 25 on thethermostat I5 will be broken. Hence, the heater 45 will not supply heattothe bimetal 35 to maintain the bimetalin engagement with theinsulating piece'32a carried by the contact arm 32. However, if theswitch arm 41 of the combustion responsive device 46 moves intoengagement with the hot contact 49 in response to the establishment ofthe combustion, before the bimetal 35 has cooled sufiiciently to tripthe contacts 33 and 34 to open position, then a circuit for the heater45 may be traced as follows:

- From the line wire |2 through conductor 55',

switch arm 3|, contacts 33 and 34, switch arm 32, conductor 56,electrode 2|, mercury 23, electrode 20, resistance 53, conductor 66,contact 49, contactarm 41, conductor 58, heater and conductor 59 to theother line wire l3. If switch arm 41 should stick to cold contact 48 theabove circuit will not be closed and bimetal 35 will open the switch 33,34. It will be noted that the resistance 53 is now in series with theheater 45. This will result in the emanation of less heat from theheater 45 and hence the bimetal 35 will cool off an amount determined byresistance 53.

It is desired that this cooling will not move the bimetal 35 out ofengagement with the insulating block 32a but will be just suificient toseparate the contact 5| from the contact blade to end of the contactblade 56 to be hereinafter break the ignition circuit which wasenergized in the ignition circuit previously pointed out. 'iIehis is thenormal running condition of the sys- In the event that there is a flamefailure or that combustion does not take place upona call for heat bythe thermostat IS, the contact blade 41 will not engage the contact 49and there will be no circuit to the heater-45 forthebimetal 35. Whenthis condition occurs the bimetal 35 will cool off and the upper endthereof will warp toward the right until it moves from beneath theinsulating piece 32a. thus permitting the contacts 33 and 34 to separateand shut down the system.

After the system has been shutdown due to some undesirable condition thesafety switch 30 must be manually reset. Any of several conventionalreclosing means could be utilized and therefore none have been shown inthe drawing.

In the event that the heater 45 should burn out it will be apparent thatthe bimetal 35 would move from beneath the insulating piece 32a-topermit the safety switch toopen. In the event the heater 40 for thecompensating bimetal 36 should burn out the bimetal 35 would be moved inthe opposite direction from beneath the insulating piece 320. by thewarping of the bimetal 36 to permit opening of the safety switch. Henceit is seen that protection is given for the burning out of either of theheaters for the safety switch. After a normal burner operation thethermostat I will become satisfied and move into the positionshown inFigure 1 to set up the original heating circuit for-the bimetal 35through the cold contact 48 of the combustion. responsive switch. If thecontact 41 should stick to the hot contact 49 and not engage the contact48 the heater 45 will not be energized and the bimetal 35 up untilmanual attention has been given to the system.

combustion. It is also fully anticipated that, by properly selecting thecasing I 28 forthe helix I25, a differential temperature may bemaintained between the two helixes whereby a small heater I35 would besuflicient to prevent opening of the safety switch even though thecombustion responsive element were subjected to a wide variation of 0temperature.

Referring now to Figure 2, burnermotor I00 and ignition means IOI aresupplied with electrical energy fromline wires I02 and I03. A thermostatI05 carries a snap acting mercury switch I06 which has contacts I01 andI08 which are closed when the thermostat is in the cold position andcontacts I09 and H0 which are closed by the mercury when the-thermostatis in the hot 'posi tion. A safety switch II5 has a contact arm II6which is relatively rigid, a flexible contact arm II! which is biased soas to open the contacts I I8 and I I9 and an arm I which is moved by acombustion responsive device I2I and isadapted .to engage an insulatingpiece I IIa carried on the contact arm Hi to maintain the safety switchclosed under normal operating conditions.

i The combustion responsive device I2I serves as a timing means andcomprises a bimetallic helix I22 which is wound so as to-cause thecontact arm I20 to rotate toward the left when the helix I22.

cools off and to rotate the arm I20 toward the right when the bimetallichelix I22 is heated. A

. rod I23 is secured to the left end of the helix I22 and to the armI20. A second helix I25 is secured to the helix I22 at the point I26.The helix I25 is wound oppositely to the helix I22 so that l the twohelixes will rotate in opposite directions when heated. The helix I25 ismounted at I21 to a casing I28. Therefore, because the two helixesrotate equally and oppositely, one end of the helix I25 being secured tothe casing and the opposite end of the helix I22 being connected to therod I23 the rod I23 will not be rotated due to changes in ambienttemperatures which affect both of the helixes in'the same degree. Aheater I30 normally supplies heat to the compensating helix I25 becauseit is connected across the line wires I02 and I03 by conductors I3I andI32. A heater I35 supplies heat to the helix I22 when the thermostat I05is in the hot position as shown in the drawing. When the thermostat I05is in the cold position no heat will be supplied to the helix I22 thatby exposing the helix I22 to a lesser degree of flame, as for examplethrough a window directed at the flame itself, rather than locating thebimetallic helix in the stack, will affect an economy in electricitysupplied to the heater I35 in Operation of Figure 2 With the parts inthe positionshown the thermostat I05 is satisfied and a circuit for theheater I 35 may be traced as follows: From the line wire I02 throughconductor I50, switcharm H6, contacts H8 and H9, contact arm 1,conductor I5I, electrodes I09 and H0, conductor I52, heater I35 andconductor I53 to the other line wire I03. At this time heat will besupplied to the helix I22 so that the arm I20 will be maintained inengagement with the insulating piece II'Ia to prevent opening ofthe-contacts H8 and H9 of the safety switch I I5.

Assuming now that the thermostat I05 cools so as to cause the contactsI09 and. H0 to open and the contacts 'I 01 and I00 to close with a rapidaction due to the fact that the mercury. within the switch must passover an indentation in the bottom of the mercury switch. A circuit maynow be traced for the motor and ignition means as follows: From linewire I 02, conductor I50, switch arm Il6, contacts H8 and II9, contactarm II'I, conductor I5I, electrodes I 08 and I0I, conductors I54, I55,motor I00, and conductor I56 to the other line wire I03. A circuit forthe ignition may be traced from the conductor I54,

through conductor I5'I, ignition means IOI, and

conductor -I 58 to the line wire I03.

Because the electrodes I09 and H0 are unbridged when the thermostat I05is in the cold position there will be no energy supplied to the heaterI35. In the event that flame doesnot occur in the combustion chamber thehelix I22 will cool off to cause the arm I20 to move out from beneaththe insulating piece H111 and permit the contacts H8 and H9 of safetyswitch II5 to open. However, if flame occurs before this section takesplace thentheheat of the fiam'e,

willaffect the helix I22 in a manner to cause the arm I20 to remain inengagement with the insulating piece IIIa to keep the contacts H8 and H0closed. Hence, it is seen that means are provided whereby a safetyswitch is combined with a combustion responsive switch to effect controlin response to the presence of combustion in a combustion chamber upon acall. for heat. 0

- In the event of flafiie failure when the thermostat I05 has themotorand ignition means in 0 .contacts I I8 and H9 to open there-byshutting. down the system. Any suitable means can be that the heatsupplied to the helix I22 by the,

heater I35 in some installations may need to} be substantially thesameas the heat supplied by operation, the combustion responsive helix I22will cool off to move the arm I20 out of engagement with the insulatingpiece I I'Ia to permit the used for manually-resetting the system onceit has been opened and therefore no means have been shown. p

, If either one of the heaters I30 or I 35 should burn out of thecontacts I I8 and I I9 will be permitted to open because the arm I20 canmove from beneath the insulating-piece II'Ia in either direction.

In the event of power failure in either of the. systems shown in Figure1 or Figure 2 there will be no drop out of the safety switches. When thepower fails in the system shown in Figure 1 both system, in combination,

' means including a first exists.

of the heaters 40 and 45 will be deenergized and, inasmuch as thebimetals 35 and 36 affected by the heaters warp in opposite directionsthey will in temperature affecting both bimetals.

While I have shown two preferred embodiments which my invention maytake, it is obvious that many modifications will occur to those skilledin the art. Many modifications utilizing timing by cooling in, acombustion responsive control device while still preventing drop out onpower failure will become apparent to those skilled in the art. Hence Ido not wish to be limitedby those forms shown and described but by thespirit and scope of the appended claims and the status of the prior art.

I claim as my invention:

1. In a burner control system comprising an electrically operable fuelcontroller and a controlling circuit therefor including a normallyclosed safety switch, in combination, timing means including a firstelement movable in a first direction upon heating and in a seconddirection upon cooling to mechanically open said safety switch when cooland to hold said safety switch closed when hot, a continuously heatedsecond compensating element operatively con! nected to said firstelement to compensate it for changes in ambient temperature, and meansfor causing heating of said first element when said controlling circuitis open but not when said circuit is closed, said first element beingheated as a result of successful combustion.

2. In a timing device for a combustion control normally closed switchmeans in circuit with a fuel controller, timing element movable in afirst and in a second direction said circuit when moved direction uponheating upon cooling to open beyond a predetermined range of movement, a

continuously heated second compensating element associated with saidfirst element and movable in said second direction upon heating and insaid first direction upon cooling, said second element being adapted tocompensate said first element for ambient temperature variations undernormal operating conditions of said combustion controller system, meansfor heating said first element under normal operating conditions of saidcombustion controller system to prevent opening of said switch means,and means associated with said timing means for causing said switchmeans to open when an abnormal condition 3. In a fuel burner controlsystem, in combination, an electrically operable fuel controller, a

circuit therefor, circuit control means to open and close said circuit,a normally closed safety switch associated with said circuit in a mannerto interrupt said circuit, timing means including an element movable ina first direction upon heating and in a second direction uponcooling,said element being associated with said safety switch in a manner toopen said safety switch upon movement of said element beyond apredetermined range of movement, heating means to supply heat to saidelement, combustion responsive means movable between hot and coldopening of said safety switch under normal operating conditions of saidsystem, an electrically operable fuel ignition circuit controlled bysaid element, and means for affecting the heat capacity of said heatingmeans to effect control of said ignition circuit when said combustionresponsive means moves between hot and cold posions.

4. In a. fuel burner control system, in combination, fuel burner means,an electrically operable fuel controller including ,a circuit therefor,a normally closed safety switch operable to interrupt said circuit,timing means including an element comprising means responsive to heatfrom the fuel burner and being movable in a first direction upon heatingand in a second direction upon cooling, said element being operable toopen said safety switch upon movement of said element beyond a.predetermined range of movement,

completing a circuit to said heating means andbreaking said circuit tosaid fuel controller.

5. In a fuel burner control system, in combination, an electricallyoperable fuel controller for fuel burner means and including a circuittherefor, a normally closed safety switchoperable to interrupt saidcircuit whenever the safety switch opens, timing means including anelement comprising means responsive to heat from the fuel burner andbeing movable in a first direction upon heating and in a seconddirection u'pon cooling, said element being operable to open said safetyswitch upon movement of said element beyond a predetermined range ofmovement, heating means to supply heat to said element, conditionresponsive means movable between a plurality of positions, one of saidpositions completing a circuit to said fuel controller for initiatingburner operation and breaking a circuit to said heating means to therebyrender said element dependent for heat upon said fuel burner, andanotherof said positions completing a circuit to said heating means andbreaking said circuit to said fuelcontroller to terminate burneroperation, compensating means associated with said element movable insaid second direction upon heating and said first direction upon coolingto thereby compensate said element for variations in ambienttemperature, and electricheating means associated with said compensatingmeans to prevent opening of said safety switch upon power failure.

6. In a fuel burner control system, in combination, a normally closedsafety switch, thermal timing meansoperable upon cooling to open saidsafety switch, said timing means being so located positions forcontrolling the supply of heat to is operating, control means to supplyheat to said timing means and when said burner is not operating, andcompensating means associated with said timing means -for preventingsaid safety switch from opening due to power failure.

8; In a burner control system comprising an electrically operable fuelcontroller and a controlling circuit therefor including a normallyclosed safety switch, in combination,-a thermal element associated withsaid safety switch, a heater for heating said thermal element to maintamsaid safety switch closed, said safety switch being opened when saidthermal element is cooled, a combustion responsive device movablebetween hot and cold contact positions in response to combustion, and athermostat movable between hot and cold contact-positions in re-' sponseto ambient temperature, the hot contact of said thermostat and the coldcontact of said combustion responsive device'being adapted to cooperateto control said heater when said fuel controller is not in operation,the cold contact of said thermostat and the hot contactof saidoperatively connected at its first end with said safety switch to holdthe same closed when hot and to open the same when cool, a seconddistortable bimetal fixed at its first end and secured at its secondendto the second end ofsaid first bimetal and movable in directionsopposite with ..respect thereto upon heating and cooling to combustionresponsive device being adapted to when said fuel tain said safetyswitch closed, said safety switch being opened when said thermal elementis cooled, a combustion responsive device movable between hot and coldcontact positions in response to combustion, a thermostat movablebetween hot and cold contact positions" in response to ambienttemperature, the hot contact of said thermostat and the cold contact ofsaid combustion responsive device being adapted to cooper- .ated timingmeans including means for supplying ate to control said heater when saidfuel contrailer is not in operation, the cold contact of said thermostatand the hot contact of said combustion responsive device being adaptedto cooperate to control said heater when said 'fuel controller is inoperation, ignition control means 1 associated with said thermalelement, and resistance means associated in circuit with said heater andthe hot contact of said combustion responsive meansfor controlling saidignition control mean by causing said thermal element to move only apredetermined amount when the resist-* ance means is placed in circuit.a

10. Ina burner control system comprising an electrically operable fuelcontroller and a controlling circuit therefor including a normallyclosedsafety switch, a normally heated first distortable bimetal movable in afirst direction upon heating and in a second direction upon coolingthereby compensate the same for fluctuations in ambient temperature, anelectric heater adjacent said second bimetal for continuously heatingthe same, an ambient temperature responsive thermostat, means forheating said first bimetal, and switch means operable by said thermostatfor controlling the supply of heat to said first bimetal.

11. A fuel burner control system comprising in combination, hot and coldswitches, a heat demandresponsive device for opening the hot and closingthe cold switch on a demand for heat andopening the cold and closing thehot upon becoming satisfied, an electrical fuel feeding device, acircuit therefor including'said cold switch, a safetyswitch in controlof said fuel feeding device, a thermal timer which when cold opens saidsafety switch, means for maintaining' a supply "of heat to said thermaltimer during a demand for heat by said responsive device, said lastnamed means including saidcold switch, said supply of heatbeingdependent upon the establishment of combustion, and a heatingcircuit for said thermal timer including saidhotswitch for maintainingsaid timer in .its hot position while said responsive device issatisfied.

'12. A burner control circuit in combination comprising, fuel supplymeans and a circuit including control means therefor, thermally operheat thereto at a first value when the fuel supply circuit is opened bythe controlmeans and to supply the timing means with heat at a secondvalue upon the establishment of combustion, a safety switch in the fuelcontrol circuit which is maintained in a closed position by the i saidtiming means when the timing means is supplied with heat within-apredetermined range including said first and second values and which isopened when the timing means is not supplied with heat sufllcie'nt tomaintain it at a tempera-.

ture within said range, combustion responsive means for controlling thesupply of heat to said timing means to maintain the supply at the saidsecond value when combustion is established,

and ignition means controlled by said timing. means for operation of theigniter only when the supply of heat to the timing means ismaintained'at said first value.

'cir'r'oan r. HOLMES,

